ABSTRACT Anger and aggression are serious and frequent complicating factors in the treatment of post-traumatic stress disorder (PTSD). A host of studies now demonstrate that interpersonal aggression and anger are: i) strongly associated with post-traumatic stress disorder (for meta-analysis, see Orth & Wieland, 2006); ii) particularly pernicious among individuals with combat-related PTSD (Novaco & Chemtob, 2002); and, iii) critical barriers to effective treatment in combat-related PTSD (Forbes et al., 2003; Forbes et al., 2008). Despite the detrimental impact that anger and aggression have on the lives of combat veterans with PTSD, and despite the barrier that anger and aggression pose to treatment and recovery, very little is understood about the neurobehavioral pathology underlying interpersonal aggression in PTSD, or the capacity of individuals with PTSD to engage in cooperative interactions more generally. The broad goal of the proposed research is to address these areas. That is, we seek to identify objective behavioral and neural metrics of aggression that contribute to impaired social interactions of individuals with combat- related PTSD. To achieve this goal, the proposed project seeks to: 7 Quantify behavioral decisions and associated neural activity during aggressive and non- aggressive interpersonal exchanges among veterans with PTSD and combat-matched control veterans. 7 Quantify behavioral decisions and associated neural activity during cooperative and non- cooperative interpersonal exchanges among veterans with PTSD and combat-matched control veterans. 7 Explore whether diagnostic differences in aggression and cooperation in PTSD are related to diminished function of neural structures associated with understanding the thoughts and intentions of social partners. The development of objective neurobehavioral measures of interpersonal difficulties associated with combat-related PTSD will facilitate early identification of veterans in need of treatment, and may aid in design and implementation of targeted therapeutic interventions.